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Evening all, I wonder if someone can share any thoughts on my situation?
I sent the below email to Octopus in January which was the first opportunity when I could see how my 9kw Daikin installed last June was performing at or below the design temperature. I'm now in a situation where the Octopus heat loss design estimates my heat loss at ~8.5kw and my own Heat Punk heat loss is 6.6kw with more accurate inputs and air changes (not all rooms in my house have trickle vents on windows, the kitchen doesn't have an extractor which extracts externally etc). The measured heat loss from EmonCMS is ~4-5kw to maintain 21*C at an average outdoor temperature of -4*C. I spoke to Octopus today and they are waiting on MCS to confirm whether 'measured heat loss' is a suitable substitute to the various heat loss calculation methodologies / standards that exist. Having read some of the MCS standards I believe they focus solely on designed heat loss, not measured heat loss (the latter of course being more accurate). Octopus stated today their survey doesn't allow modifying any air changes/hr for each room so they are limited to the standard assumptions (which of course can lead to inaccurate results).
I'd welcome any insights or advice from others - I'd like Octopus to swap the 9kw high capacity unit (which is a software limited 16kw unit) with the 8kw low capacity unit which can modulate down lower to prevent cycling.
I called on Saturday about the noise from the 9kw Daikin installed in June this year and enquired about removing it from the wall bracket and ground mounting instead if I install a solid concrete base. I have subsequently reviewed performance of the 9kw unit (and specificallyheatproduced to maintain 21*C internal temperature). On both Friday and Saturday, the hourlyheatoutput to maintain 21 degrees (including hot water cycle) is 4.59kw and 3.91kw respectively. This is the first occasion that theheatpump has operated near to the design temperature as shown in the following screenshots, Friday reaching -4.6*C outdoors with an average over both days being the same at -2.6*C, Saturday was -5.9*C at its coldest point.
To minimise the possibility of solar gain impacting this, I have also taken a screenshot of a 9hr period covering 6pm-3am which works out at 4.192kwheatloss(per hour). This was with an average external temperature of -4*C and a flow rate of 45*C which resulted in cycling above and beyond the defrost cycles (off from midnight for an hour). I have subsequently turned the flow rate down even further on the weather dependent curve from 45*C to 40*C (design flow temp was 50*C at -3*C) as I am still experiencing symptoms of an oversized unit which is cycling even at or below the design temperature.
Please can you now swap the unit with the 8kw version which will be entirely adequate to theheatlossof my home? If at an average external temperature of -4*C the 9kw unit cannot modulate down low enough to maintain a constant output, this is surely a sign the 9kw unit is too large? During the 9hr period theheatpump shut off 3 times because the room temperature was reached and theheatoutput from theheatpump could not reasonably be reduced any further.
I am acutely aware that I have paid for several instalments on a credit card and am therefore covered by section 75 protection. I hope thatOctopuswill be amicable and replace the 9kw unit with the 8kw Daikin which is quieter and can modulate down low enough to deliver a constantheatoutput. I will prepare a concrete base in anticipation of this in order that the 8kw unit can also be ground mounted (the 9kw Daikin on the wall mounts is waking me up at night due to excessive noise from it cycling and the compressor ramping up / down repeatedly).
My thoughts are - good luck, you seem to have a reasonable argument for the replacement. That said Im not sure you could prove the current one is unfit for purpose so they may well decline, but worth a go.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
There have been several people on the OpenEnergyMonitor forums who have persuaded Octopus to replace their 9kW or 11kW Daikin with a smaller 6kW or 8kW Daikin. Take a look at this.
@jamespa thanks, it's way off of the MCS performance estimate and I think if it ended up in Court I could construct a sound case to justify it's not fit for purpose (based on efficiency, wording on the contract etc)
@big_si As has been mentioned you are not the first with this problem. Several 🐙 clients have had Daikin 9s changed for Daikin 8s. The first was Matt Drummer who is over on OE Monitor.
The 9kw is a 16 kw restricted by software and is famously juicy although there are people running them very efficiently. The restriction means they don't have the modulation range which is a pain.
The 4/6/8 are the same - all are 8s restricted by software but for some reason it doesn't have the same impact. All 3 modulate down very nicely. I have the 6kw Daikin and I am very happy with it. I run it on pure weather compensation and the compressor never turns off and it runs low without complaining or cycling.
Key for you is building a case with evidence so do talk to the other guys over on the OEM forum. Best of luck. 🐙 are pretty good if you make a strong, logical case.
@lucia thanks for the reply, I think I've now got sufficient evidence that it needs replacing particularly OEM data when it was operating at design temperature which I did not have last year when Octopus refused to replace it at my first request. I've since raised with NAPIT and MCS as additional levers. I just want the system to perform as intended and the 9kw isn't meeting expectations in that regard and hopefully Octopus learn from this with future surveys to reduce rework and increase customer satisfaction.
9kw monster swapped with the 8kw unit today - it's whisper quiet and running a treat so far! Well worth persevering with NAPIT as Octopus were reluctant to swap out the 9kw. Had to tweak the EmonCMS flow temperature sensor to before backup heater (as the 8kw doesn't have a backup heater) and updated the details on heatpumpmonitor.org
Looking forward to seeing how it performs next winter 🙂
@big_si thanks for the update. It’s still forecast to be unseasonably chilly for a few more days so you may get some insights. But good to hear you’re happy with the new smaller unit. Keep us updated.
